Method for DNA defined etching of a graphene nanostructure

ABSTRACT

Disclosed is a method for etching graphene using a DNA sample of a predetermined DNA shape. The DNA sample is preferably placed onto a reaction area of a piece of highly oriented pyrolytic graphite (HOPG), and both the DNA sample and HOPG are then preferably placed into a humidity-controlled chamber. Humidity is preferably applied to the HOPG to produce a film of water across the surface of the DNA sample. Electrical voltage is also applied to the HOPG to create potential energy for the etching process. After the etching is completed, the reaction area is typically rinsed with deionized water.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/480,774 filed Sep. 9, 2014, now U.S. Pat. No. 9,981,851,which is a continuation of U.S. patent application Ser. No. 13/630,975filed Sep. 28, 2012, now U.S. Pat. No. 8,858,778, which claims thebenefit of U.S. Provisional Patent Application 61/588,556 filed Jan. 19,2012, the entire contents of each of which are expressly incorporatedherein by this reference.

FIELD

This invention generally relates to a method for etching graphene. Inparticular, the invention is an etching method for graphene-basedmaterials on a nanoscale by applying a voltage potential using DNAsamples.

BACKGROUND

Graphene has rapidly received significant attention since its discoveryin 2004 due to its unique electrical, mechanical, and physicalproperties. Examples of such include low resistivity and high carriermobilities. Researchers have discovered, for example, that electrons cantravel substantially faster in graphene than in silicon by approximatelyone hundred times due to graphene's low resistivity. A single-atom-thicksheet of graphite, for instance, provides a resistivity of about 1.0micro-Ohm per cm, which is approximately 35% less than the resistivityof copper, the previously lowest resistivity material known at roomtemperature. This low resistivity in graphene therefore provides higherconductivity for graphene-based applications, which is a big advantagefor semiconductor applications that require rapid switching.

Regarding carrier mobility, graphene's limit to mobility of electronsalso surpasses silicon. The limit of electron mobility in graphene isset by thermal vibration of the atoms and is approximately 200,000cm²/Vs at room temperature. Silicon, on the other hand, is about 1400cm²/Vs. Because current graphene applications utilize only 10,000cm²/Vs, potential exists to maximize graphene-based applications toattain the 200,000 cm²/Vs limit.

Despite these advantages, graphene is usually constructed with channelshaving a nanoscale line width. Thus, to take advantage of thesegraphene-based applications, graphene fabrication generally requires theproduction of nanowires with a line width of approximately 1-2 nm inorder to have a silicon band gap (i.e., approximately 1.11 eV). Thiscauses problems because presently available semiconductor processingtechniques make it impossible to cut graphene to such a narrow nanoscaleline width, which is typically less than 3 nm. Additionally,conventional methods are much slower, requiring each point to be etchedaway by electrochemically reacting in a serial fashion. Further, theseconventional methods typically rely on etching through a mask that hasbeen fabricated using top-down lithography, which is known forpreventing nanoscale resolution of patterns.

Therefore, what is needed is a new method for fabricating graphene at ananoscale. The preferred method would be faster, utilizes a “bottom-up”approach, and uses DNA samples for etching.

SUMMARY

To minimize the limitations in the prior art, and to minimize otherlimitations that will become apparent upon reading and understanding thepresent specification, the present invention discloses a method foretching graphene using DNA samples.

One embodiment of the present invention is a method for etching agraphene nanostructure, the steps comprising: providing a piece ofhighly oriented pyrolytic graphite; wherein the piece of highly orientedpyrolytic graphite has a first window, a second window, and a thirdwindow; wherein the first window and the second window include one ormore electrode contacts configured to receive an electrical voltage;wherein a portion of the third window includes a reaction areaconfigured to receive a DNA sample; depositing the DNA sample to thereaction area; placing the piece of highly oriented pyrolytic graphitein a humidity controlled chamber; applying a relative humidity to thepiece of highly oriented pyrolytic graphite; and applying an electricalvoltage across the first window and the second window. Preferably, thepiece of highly oriented pyrolytic graphite is coated with a resist.Preferably, the first window, the second window, and the third windoware etched by a scanning electron microscope using electron-beamlithography. The first window and the second window are typicallypositioned at approximately 600 to 1000 mirometres (mircometers ormicrons) apart, but are preferably positioned approximately 800micrometres apart. The method for etching a graphene nanostructure mayfurther comprise the step of: analyzing the first window, the secondwindow, and the third window with an atomic force microscope. The methodfor etching a graphene nanostructure may further comprise the steps of:heating and melting the DNA sample and cooling the DNA sample to roomtemperature. The method for etching a graphene nanostructure may furthercomprise the step of diluting the DNA sample to a buffer solution.Typically, the buffer solution is approximately 0.5 to 1.5 molars ofpotassium chloride (preferably 1 molar); approximately 8 to 12millimolars of tris(hydroxymethyl)aminomethane hydrochloride (preferably10 millimolars); and approximately 8 to 12 millimolars ofethylenediaminetetraacetic acid (preferably 10 millimolars) (but anytype of buffer solution may be used to provide ions for stabilizing theDNA sample due to the DNA sample's strong negative charge and itsability to fix the pH levels). Preferably, the electrical voltage is avoltage gradient of approximately 2 to 6 V/mm (preferably 4 V/mm) TheDNA sample is preferably a double-stranded unmethylated lambda DNA. Themethod for etching a graphene nanostructure may further comprise thestep of rinsing the DNA sample in warm deionized water.

Another embodiment of the present invention is a method for etching agraphene nanostructure, the steps comprising: providing a piece ofhighly oriented pyrolytic graphite; wherein the piece of highly orientedpyrolytic graphite has a first window, a second window, and a thirdwindow; wherein the first window and the second window include one ormore electrode contacts configured to receive an applied voltage;wherein a portion of the third window includes a reaction areaconfigured to receive a DNA sample; depositing the DNA sample to thereaction area; heating and melting the DNA sample; cooling the DNAsample to room temperature; diluting the DNA sample to a buffersolution; applying the buffer solution to the reaction area; incubatingthe reaction area; rinsing the reaction area with deionized water toremove the buffer solution and an excess of the DNA sample; placing thepiece of highly oriented pyrolytic graphite in a humidity controlledchamber; applying a relative humidity to the piece of highly orientedpyrolytic graphite; applying an electrical voltage gradient across thefirst window and the second window for approximately one to two minutes;and rinsing the piece of highly oriented pyrolytic graphite in warmdeionized water. Preferably, the first window; the second window; andthe third window are etched by a scanning electron microscope usingelectron-beam lithography. Preferably, the method for etching a graphenenanostructure may further comprise the step of: analyzing the firstwindow, the second window, and the third window with an atomic forcemicroscope. The first window and the second window are preferablypositioned approximately 600 to 1000 micrometres apart. Preferably, theDNA sample is a double-stranded unmethylated lambda DNA. The heating andmelting step may be performed for approximately eight to twelve minutes(preferably eight minutes) at approximately 70 to 110° C. (preferably90° C.) (but any amount of time may be used such as one minute to anhour). Preferably, the buffer is approximately 0.5 to 1.5 molars ofpotassium chloride; approximately 8 to 12 millimolars oftris(hydroxymethyl)aminomethane hydrochloride; and approximately 8 to 12millimolars of ethylenediaminetetraacetic acid acid (but any type ofbuffer solution may be used to provide ions for stabilizing the DNAsample due to the DNA sample's strong negative charge and its ability tofix the pH levels). The applied relative humidity may be approximately60 to 90%, but preferably 75% (but any amount of relative humidity(e.g., 0 to 100%) and/or temperature (e.g., 0 to 200° C.) may be used).

Another embodiment of the present invention is a method for etching agraphene nanostructure, the steps comprising: providing a piece ofhighly oriented pyrolytic graphite; wherein the piece of highly orientedpyrolytic graphite is coated with a polymethylmetaacrylate resist;wherein the piece of highly oriented pyrolytic graphite has a firstwindow, a second window, and a third window; wherein the first window;the second window; and the third window are etched by a scanningelectron microscope using electron-beam lithography; wherein the firstwindow and the second window include one or more electrode contactsconfigured to receive an electrical voltage; wherein the first windowand the second window are positioned approximately 600 to 1000micrometres apart; analyzing the first window, the second window, andthe third window with an atomic force microscope; wherein the firstwindow and the second window include one or more electrodes configuredto make electrical contact; wherein a portion of the third windowincludes a reaction area configured to receive a double-strandedunmethylated lambda DNA; depositing the double-stranded unmethylatedlambda DNA to the reaction area; heating and melting the double-strandedunmethylated lambda DNA for approximately eight to twelve minutes atapproximately 70 to 110° C. (but any amount of time may be used such asone minute to an hour); cooling the double-stranded unmethylated lambdaDNA to room temperature; diluting the double-stranded unmethylatedlambda DNA with a buffer solution; wherein the buffer solution isapproximately 0.5 to 1.5 molars of potassium chloride; approximately 8to 12 millimolars of tris(hydroxymethyl)aminomethane hydrochloride; andapproximately 8 to 12 millimolars of ethylenediaminetetraacetic acid(but any type of buffer solution may be used to provide ions forstabilizing the DNA sample due to the DNA sample's strong negativecharge and its ability to fix the pH levels); applying the buffersolution to the reaction area; incubating the reaction area forapproximately twenty to forty seconds (preferably thirty seconds);rinsing the reaction area with a deionized water to remove the buffersolution and an excess DNA; analyzing the third window with the atomicforce microscope; placing the piece of highly oriented pyrolyticgraphite in a humidity controlled chamber; applying a relative humidityof approximately 60 to 90% to the piece of highly oriented pyrolyticgraphite (but any amount of relative humidity (e.g., 0 to 100%) and/ortemperature (e.g., 0 to 200° C.) may be used); applying an electricalvoltage gradient of approximately 2 to 6 V/mm across the first windowand the second window for approximately one to two minutes; and rinsingthe piece of highly oriented pyrolytic graphite in warm deionized water.

It is an object of the present invention to provide a method forcontrolled etching of graphene based materials. The method or processpreferably works on a nanometer scale in a matter of seconds underambient conditions, but may also take up to several minutes or even oneor more hours, and any amount of temperature may be applied such as 0 to200° C.

It is an object of the present invention to provide a method forcontrolled etching of nanoscale graphene materials by using a bottom-upapproach with the use of a self-assembled etch mask constructed of DNAsamples.

It is an object of the present invention to overcome the limitations ofthe prior art.

These, as well as other components, steps, features, objects, benefits,and advantages, will now become clear from a review of the followingdetailed description of illustrative embodiments, the accompanyingdrawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings are of illustrative embodiments. They do not illustrate allembodiments. Other embodiments may be used in addition or instead.Details which may be apparent or unnecessary may be omitted to savespace or for more effective illustration. Some embodiments may bepracticed with additional components or steps and/or without all of thecomponents or steps which are illustrated. When the same numeral appearsin different drawings, it refers to the same or like components orsteps.

FIG. 1 is a block diagram of one embodiment of the method for etching agraphene nanostructure.

FIG. 2 is an illustration of one embodiment of the method for etching agraphene nanostructure and shows electrical leads positioned above thefirst window and second window of the highly oriented pyrolyticgraphite.

FIG. 3 is an illustration of one embodiment of the method for etching agraphene nanostructure and shows a detailed view of the reaction area ofthe third window after˜voltage and a relative humidity are applied tothe reaction area.

FIG. 4 is a schematic of a graphene surface with a DNA sample of oneembodiment of the method for etching a graphene nanostructure and showsa double layer formation when humidity is applied to the highly orientedpyrolytic graphite.

FIG. 5 is a graph of one embodiment of the method for etching a graphenenanostructure and shows the distance of a water film with respect torelative humidity levels.

FIG. 6 is a graph of one embodiment of the method for etching a graphenenanostructure and shows the thickness of a water film with respect to avoltage potential.

DETAILED DESCRIPTION

In the following detailed description of various embodiments of theinvention, numerous specific details are set forth in order to provide athorough understanding of various aspects of one or more embodiments ofthe invention. However, one or more embodiments of the invention may bepracticed without some or all of these specific details. In otherinstances, well-known methods, procedures, and/or components have notbeen described in detail so as not to unnecessarily obscure aspects ofembodiments of the invention.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the invention. As will be realized, theinvention is capable of modifications in various obvious aspects, allwithout departing from the spirit and scope of the present invention.Accordingly, the graphs, figures, and the detailed descriptions thereof,are to be regarded as illustrative in nature and not restrictive. Also,the reference or non-reference to a particular embodiment of theinvention shall not be interpreted to limit the scope of the invention.

The method of the present invention etches graphene based materialsusing a DNA sample. Specifically, a DNA sample is typically placed on areaction area of a piece of highly oriented pyrolytic graphite (HOPG),where both the DNA sample and HOPG are later placed in ahumidity-controlled chamber. Humidity is generally applied to the HOPGand DNA sample to produce a water film, which typically forms across thesurface of the DNA, but not on the surface of the HOPG. Electricalvoltage is then preferably applied to the HOPG, thereby causing thevoltage and water film to provide the potential energy for the etchingprocess. Once the etching is completed, the reaction area may be rinsedwith deionized water.

The application of humidity to the DNA sample with the HOPG is preferredbecause it typically provides the voltage potential for the etchingprocess. For instance, a negatively-charged object placed in watercontaining both positive and negative ions generally acquires ascreening layer that constitutes an electrochemical capacitance, whichtypically contains a first layer and second layer (i.e., double layer).The first layer of immobilized positive ions (i.e., the inner Helmholtzplane) forms near the negatively-charged surface of the DNA sample witha voltage potential generally increasing linearly up to that plane. Onthe other hand, negatively charged ions assemble at the second layer(i.e., the outer Helmholtz plane) with the voltage potential generallydecreasing linearly up to that plane. A final layer, (i.e., thediffusive layer) forms, which typically connects the second layer (i.e.,the outer Helmholtz plane) to the bulk of the water. This final layergenerally has a voltage potential that exponentially tends to be zero.

In the present invention, however, unlike placing the entire HOPG inliquid or water, a thin water film is typically formed on the moleculesof the DNA sample. Water film typically forms on the DNA, but does notusually form on the graphene surface. This typically occurs because DNAis hydrophilic while the graphene surface is hydrophobic. As a result,the water film of the present invention provides a finite voltage, whichis used as the voltage potential for the etching process. Although theuse of humidity in the present invention may specifically refer towater, it should be understood that any vapor-like substance may be usedto create the voltage potential (e.g., such as nitrogen vapor) withoutdeviating from the scope of the invention.

In the following description, certain terminology is used to describecertain features of one or more embodiments of the invention. Forinstance, the terms “graphite” or “highly oriented pyrolytic graphite”(“HOPG”) refers to graphite materials consisting of crystallites beinghighly aligned or oriented with respect to one another and havingwell-ordered carbon layers or a high degree of preferred crystalliteorientation and also even refers to any single layer or multiple layersof graphene, including without limitation, thermal pyrolytic graphiteand annealed pyrolytic graphite. The term “graphene” or “graphene film”denotes the atom-thick carbon sheets or layers that stack up to form“cleavable” layers (or mica-like cleavings) in graphite. The term “DNAsamples” refers to any manufactured and/or programmable shapeconstructed from deoxyribonucleic acid used for the graphene etchingprocess, including without limitation, double-stranded unmethylatedlambda DNA.

FIG. 1 is a block diagram of one embodiment of the method for etching agraphene nanostructure. As shown in FIG. 1, the method for etching agraphene nanostructure 100 preferably comprises the steps of: providinga piece of highly oriented pyrolytic graphite 103; creating a firstwindow, a second window, and a third window on the highly orientedpyrolytic graphite 106; heating and melting a DNA sample 109; coolingthe DNA sample to room temperature 112; diluting the DNA sample with abuffer solution 115; depositing the DNA sample into the reaction area118; applying the buffer solution to the reaction area 121; incubatingthe reaction area 124; rinsing the reaction area with deionized water127; analyzing the third window 130; applying an electrical voltage tothe first window and second window 139 and rinsing the HOPG in warmdeionized water 142. It should be understood that the method 100 mayomit certain steps and include other steps as well.

FIG. 1 shows the first step of the method for etching a graphenenanostructure 100, which is to provide a piece of highly orientedpyrolytic graphite 103. Highly oriented pyrolytic graphite (HOPG) 205(shown in FIG. 2) is generally a bulk material consisting of manygraphene layers with an exposed surface of graphite being a modelgraphene surface on a graphite substrate, but may also refer to a singlelayer or multiple layers of graphene. Preferably, the HOPG 205 is spincoated with an electron beam resist. The resist is typically a thinlayer used to transfer a circuit pattern to the semiconductor substrate,and is also preferably polymethylmethacrylate (PMMA). While HOPG 205 isthe primary material used for the present invention, it is understoodthat any type of graphite may be used such as thermal pyrolytic graphiteand annealed pyrolytic graphite.

FIG. 1 shows the next step of one embodiment of the method for etching agraphene nanostructure 100—i.e., creating a first window 220, a secondwindow 225, and a third window 230 on the highly oriented pyrolyticgraphite 106. Preferably, the creation of a first window 220, secondwindow 225, and third window 230 is performed by utilizing electron-beamlithography on the HOPG 205 with a scanning electron microscope.Specifically, the scanning electron microscope should emit a beam ofelectrons in a patterned fashion across the HOPG surface to create threewindows, which are preferably substantially square or rectangular inshape. It should be understood, however, that the three windows may bein any shape or form such as circles, triangles, octagons, and/orhexagons. Additionally, it should also be understood that the presentinvention does not require the use of windows and, alternatively, mayallow the creation of any number of windows such as four, five, and six.Preferably, the electron beam lithography selectively removes eitherexposed or non-exposed regions of the resist. This is typicallyaccomplished to create very small structures in the resist that can besubsequently transferred to the substrate material by the etchingprocess. It is important to note, however, that the present inventiondoes not require the use of resist on the HOPG. Additionally, the firstwindow 220 is typically spaced apart from the second window 225approximately 600 to 1000 micrometres apart, but is preferably spacedapart by 800 micrometres. Once the three windows are created, thewindows may be cleansed with isopropyl alcohol and blown dry. It ispreferred that the windows be imaged with an atomic force microscope toascertain their cleanliness. It is also preferred that the first window220 and second window 225 are configured to make electrical contactwhile the third window 230 is to be used as a reaction area.

FIG. 1 also illustrates the third and fourth steps of one embodiment ofthe method for etching a graphene nanostructure 100, which are: heatingand melting the DNA sample 109 and cooling the DNA sample to roomtemperature 112. A DNA sample, which is typically a double-strandedunmethylated lambda DNA, is preferably heated and melted in order toprepare the patterned DNA in a pattern configuration. The DNA sample isgenerally heated, melted, and cooled in order to separate the doublestrand of the DNA sample and to create one or more sections of thesingle stranded DNA. Although the double-stranded DNA generally has pooradhesion to the graphene, the single stranded DNA usually has highadhesion to the graphene surface. Additionally, while this embodimentutilizes a double-stranded unmethylated lambda DNA, other types of DNAmay be used.

The heating and melting process is typically performed by placing theDNA sample in a heat controlled chamber. The DNA sample also isgenerally melted when the DNA sample is heated for eight to twelveminutes at approximately 70 to 110° C. (preferably 90° C.). However, itshould be understood, that the DNA sample may be melted by any method ormeans and may take up any duration of time and temperature. After themelting step is accomplished, the DNA sample is typically cooled down toroom temperature.

FIG. 1 also shows the fifth and sixth steps of one embodiment of themethod for etching a graphene nanostructure 100, which is: diluting theDNA sample with a buffer solution 115 and depositing the DNA sample intothe reaction area 118. Specifically, when the HOPG 205 (along with theDNA sample) is cooled down to room temperature, the DNA sample isusually diluted into a buffer solution. The buffer solution is typicallyany aqueous solution that reduces the change of pH upon addition ofsmall amounts of acid or base. For example, the buffer solution of oneembodiment of the present invention typically consists of approximately0.5 to 1.5 molars of potassium chloride (preferably 1 molar of potassiumchloride); approximately 8 to 12 millimolars oftris(hydroxymethyl)aminomethane hydrochloride (preferably 10 millimolarsof tris(hydroxymethyl)aminomethane); and approximately 8 to 12millimolars of ethylenediaminetetraacetic acid (preferably 10millimolars of ethylenediaminetetraacetic acid). However, it should beunderstood that any type of buffer solution may be used. Once the DNAsample is diluted with the buffer solution, the DNA sample is preferablydeposited into the reaction area of the HOPG.

FIG. 1 also shows the next four steps of one embodiment of the methodfor etching a graphene nanostructure 100, which are: applying the buffersolution to the reaction area 121; incubating the reaction area 124;rinsing the reaction area with deionized water 127; and analyzing thethird window 130. Specifically, the buffer solution is preferablyapplied to the reaction area and typically allowed to incubate. Theincubation period may be between twenty to forty seconds (preferablythirty seconds), but any length of time may be used such as one minuteor half an hour. After the expiration of the incubation period, thereaction area is preferably rinsed with deionized water to assist inremoving the buffer solution and any excess DNA. Preferably, thereaction area is imaged to ascertain its cleanliness.

The eleventh and twelfth steps of the method for etching a graphenenanostructure 100 are placing the highly oriented pyrolytic graphite ina humidity controlled chamber 133 and applying a relative humidity tothe highly oriented pyrolytic graphite 136. Specifically, afteranalyzing the third window 130 for any excess DNA and/or buffersolution, the HOPG 205 is preferably placed into a humidity-controlledchamber. A pre-determined relative humidity is generally applied to theHOPG 205, thereby typically resulting with the formation of a thin waterfilm. It is preferred that the relative humidity be 70%, but any levelof relative humidity such as 0 to 100% may be applied. Additionally, anytemperature such as 0 to 200° C. may be used, especially since any typeof polar vapor may form on the DNA sample/HOPG.

FIG. 1 also shows the last two steps of the method for etching agraphene nanostructure 100, which is applying an electrical voltage tothe first window and second window 139 and rinsing the HOPG in warmdeionized water 142. When the HOPG 205 is placed in the humiditycontrolled chamber, two electrical leads 210, 215 (shown in FIG. 2)typically contact the first window 220 and second window 225,respectively of the HOPG 205. Preferably, an electrical voltage ofapproximately between 5 to 15V is applied to the HOPG 205 (preferably 10V) with an applied voltage gradient of approximately 2 to 6 V/mm(preferably 4 V/mm) However, it should be understood that any voltagemay be applied to the HOPG 205 without deviating from the scope of theinvention. Once the etching period is completed, the HOPG 205 may berinsed in warm deionized water. The etching period preferably lasts forapproximately one minute but any time duration may be used for etching.Additionally, the rinsing period preferably lasts for approximatelytwenty minutes, but any time duration may be used for rinsing.

FIG. 2 is an illustration of one embodiment of the method for etching agraphene nanostructure and shows electrical leads positioned above thefirst window and second window of the highly oriented pyrolyticgraphite. As shown in FIG. 2, one embodiment of the method for etching agraphene nanostructure 100 preferably includes: the highly orientedpyrolytic graphite (HOPG) 205 and electrical leads 210, 215. Theelectrical leads 210, 215 are preferably any conducting mechanism thatprovides an electrical voltage to the HOPG 205. The electrical leads210, 215 preferably contact the HOPG 205 after the HOPG 205 is placed inthe humidity controlled chamber. However, the electrical leads 210, 215may also provide electrical contact prior to placing the HOPG 205 intothe humidity controlled chamber. The electrical leads 210, 215 typicallyprovide an electrical power supply of approximately 10V, but may supplyother various voltages as well such as 5 to 25V. The electrical lead 210preferably provides a ground to the first window 220 while electricallead 215 supplies the positive voltage charge (e.g., 10V) to the secondwindow 225. It should be understood, however that electrical lead 210may provide a positive voltage charge, whereas electrical lead 215 mayprovide ground. Furthermore, electrical lead 210, which generallyprovides ground, preferably includes a resistor connected in-betweenground and the HOPG. Although an 8.9 ohm resistor for a 10V power supplyis typically used, any type of resistor may be connected to ground.

Moreover, as discussed above, the HOPG 205 preferably includes a firstwindow 220, second window 225, and third window 230. The first window220 preferably includes one or more electrode contacts configured toprovide conductance and is preferably connected to an electrical lead210. Similarly, the second window 225 likewise preferably includes oneor more electrode contacts and is also preferably connected to anotherelectrical lead 215. It is important to note that, although the presentinvention recites the use of electrodes, electrodes may not be requiredfor the present invention, as any conducting sublayer may be positionedbeneath one or more layers of graphene, as this may be a preferredmethod for the manufacturing process.

Additionally, while FIG. 2 shows electrical lead 210 contacting thefirst window 220 and electrical lead 215 contacting the second window225, it should be understood that electrical lead 215 may contact thefirst window 220 and electrical lead 210 may contact the second window225. Additionally, while FIG. 2 shows the third window 230 in-betweenthe first window 220 and second window 225, the third window 230 may bepositioned anywhere on the HOPG such as left or right of the firstwindow 220 and/or second window 225. As discussed above, the firstwindow 220 and second window 225 are preferably spaced apart atapproximately 600 to 1000 micrometre, but may be separated by anydistance. The third window 230 preferably includes a reaction area, andis preferably the location where the DNA sample is inserted.

FIG. 3 is an illustration of one embodiment of the method for etching agraphene nanostructure and shows a detailed view of the reaction area ofthe third window after a voltage and a relative humidity are applied tothe reaction area. As shown in FIG. 3, one embodiment of the HOPG 205 ofthe method 100 for etching a graphene nanostructure preferably includes:a first window 220, second window 225, and third window 230. Thereaction area of the third window 230 may include one or more areaswhere etching has occurred 305, and one or more portions of excess DNA310, which have not been washed off or removed. For purposes of FIG. 3,the areas where etching has occurred 305 may be represented by thetriangular shapes, and the portions of excess DNA may be approximately14 nanometers in thickness. The present invention, however, allows theetching of any shape or form such as circles, squares, and straightlines, and portions of excess DNA may be of any thickness such asapproximately 8 to 12 nanometers.

FIG. 4 is a schematic of a graphene surface with a DNA sample of oneembodiment of the method for etching a graphene nanostructure and showsa double layer formation when humidity is applied to the highly orientedpyrolytic graphite. As shown in FIG. 4, the surface of one embodiment ofthe method 100 for etching a graphene nanostructure preferably includes:a graphene surface 403; negatively charged DNA sample 405; and doublelayer 408. The graphene surface 403 is preferably the surface area ofthe HOPG, but may be the surface of any metal or material. Thenegatively charged DNA sample 405 is preferably the DNA sample that ischarged with one or more electrically charged atom or group of atoms.The double layer 408 or electrical double layer is generally a structurethat appears on the surface of an object when it is placed into a liquidand typically refers to the three significant films of water surroundingthe charged object. The double layer 408 preferably includes an innerHelmholtz plane 410, outer Helmholtz plane 415, and diffusive region420. The inner Helmoltz plane 410 is preferably the inner layer orsurface plane that contains a layer of partially dissolved ions near thegraphene surface 403. The outer Helmoltz plane 415 is preferably a planeof fully dissolved ions that resides above the inner layer and istypically composed of ions attracted to the surface charge via thecoulomb force, electrically screening the inner Helmoltz plane 410. Thediffusive layer 420 preferably is the region that resides outside boththe inner Helmoltz plane 410 and outer Helmoltz plane 415 and generallyconnects to the bulk of the liquid. The symbol w preferably representsthe distance from the negatively charged DNA sample 405 and ispreferably represented herein in nanometers.

In general, a negatively charged object that is placed in watercontaining both positive and negative ions acquires a screening layerthat constitutes an electrochemical capacitance. This electrochemicalcapacitance of the double layer 408 is typically large, and the carbonnanotubes (which usually have a size comparable to DNA) can be utilizedeffectively for gating purposes. A layer of immobilized positive ionsforms near towards the inner Helmholtz plane 410 and the voltagegenerally increases linearly up to that plane, as shown in FIG. 6.Negatively charged ions, on the other hand, usually assemble at theouter Helmholtz plane 415 and the voltage potential generally decreaseslinearly up to that plane. The negatively charged ions in this layeralso preferably contribute to ionic conductance. At the diffusive layer420, which connects the outer Helmoltz plane 415 to the bulk of thewater, the voltage potential exponentially tends to be zero. However,because the present invention usually tends to create water films thatare exceedingly thin, the bulk limit is typically never attained, and,as a result, a finite voltage difference usually exists across the waterfilm. This finite voltage is preferably the potential that provides theenergy for the etching process.

FIG. 5 is a graph of one embodiment of the method for etching a graphenenanostructure and shows the distance of a water film with respect torelative humidity levels. As shown in FIG. 5, the graph illustrates therelative humidity with respect to the inner Helmholtz plane 430; outerHelmholtz plane 435; and diffusive region 440. When the HOPG 205 alongwith the DNA sample is placed in a humidity-controlled chamber, a filmof water generally forms on the DNA sample, but does not generally formon the graphene surface. This typically occurs because the surface ofthe DNA sample is hydrophilic—i.e., interacts with water or other polarsubstances. The graphene surface, on the other hand, is generallyhydrophobic—i.e., does not interact with water. This thickness of thewater film is generally given by the Brunauer-Emmett-Teller (BET) model.For instance, according to FIG. 5, in one embodiment of the invention,as distance w increases, the relative humidity likewise increases upapproximately to 50% at the inner Helmholtz plane 430, 70% at the outerHelmholtz plane 435, and 80% at the diffusive region 440. Distance walso increases at these regions at approximately 0.3 nm, 0.45 nm, and0.65 nm, respectively.

FIG. 6 is a graph of one embodiment of the method for etching a graphenenanostructure and shows the thickness of a water film with respect tothe voltage potential. As shown in FIG. 6, the graph illustrates thevoltage potential iv with respect to distance w, as it applies to theinner Helmholtz plane 445; outer Helmholtz plane 450; and diffusiveregion 455. As discussed above, as distance w increases, the voltagepotential iv likewise increases up to the inner Helmholtz plane 445.This is typically due to the formation of immobilized positive ions atthe negatively charged surface of the inner Helmholtz plane 445.However, voltage potential ψ decreases outside the outer Helmholtz plane450 and also at the diffusive region 455. This generally occurs becausenegatively charged ions assemble at the outer Helmholtz plane 450, whichgenerally contribute to ionic conductance.

Unless otherwise stated, all measurements, values, ratings, positions,magnitudes, sizes, locations, and other specifications which are setforth in this specification, including in the claims which follow, areapproximate, not exact. They are intended to have a reasonable rangewhich is consistent with the functions to which they relate and withwhat is customary in the art to which they pertain. Additionally, thevalues set forth in this application may also depend greatly on thequality of the graphene being used with respect to the crystallites.

The foregoing description of the preferred embodiment of the inventionhas been presented for the purposes of illustration and description.While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe above detailed description, which shows and describes illustrativeembodiments of the invention. As will be realized, the invention iscapable of modifications in various obvious aspects, all withoutdeparting from the spirit and scope of the present invention.Accordingly, the detailed description is to be regarded as illustrativein nature and not restrictive. Also, although not explicitly recited,one or more embodiments of the invention may be practiced in combinationor conjunction with one another. Furthermore, the reference ornon-reference to a particular embodiment of the invention shall not beinterpreted to limit the scope the invention. It is intended that thescope of the invention not be limited by this detailed description, butby the claims and the equivalents to the claims that are appendedhereto.

Except as stated immediately above, nothing which has been stated orillustrated is intended or should be interpreted to cause a dedicationof any component, step, feature, object, benefit, advantage, orequivalent to the public, regardless of whether it is or is not recitedin the claims.

What is claimed is:
 1. A method, comprising: providing a piece of highlyoriented pyrolytic graphite including first and second electrodecontacts configured to receive an electrical voltage, and a reactionarea configured to receive a DNA sample; depositing said DNA sample onthe reaction area of said piece of highly oriented pyrolytic graphite,wherein said DNA sample comprises double-stranded DNA or single-strandedDNA; applying a relative humidity to said piece of highly orientedpyrolytic graphite; applying said electrical voltage across said firstand second electrode contacts, thereby etching a surface of said highlyoriented pyrolytic graphite; and rinsing said etched highly orientedpyrolytic graphite in deionized water.
 2. The method of claim 1, whereinsaid piece of highly oriented pyrolytic graphite is coated with aresist.
 3. The method of claim 1, wherein said first and secondelectrode contacts are positioned approximately 600 to 1000 micrometresapart.
 4. The method of claim 1, further comprising: analyzing thereaction area with an atomic force microscope.
 5. The method of claim 1,wherein said DNA sample is a double-stranded unmethylated lambda DNA. 6.The method of claim 1, further comprising: heating and melting said DNAsample; and cooling said DNA sample to a room temperature, therebyforming a heated and cooled DNA sample, prior to depositing said DNAsample on said reaction area of said highly oriented pyrolytic graphite.7. The method of claim 6, further comprising: diluting said heated andcooled DNA sample with a buffer solution prior to depositing said DNAsample on said reaction area of said highly oriented pyrolytic graphite.8. The method of claim 7, wherein said buffer solution is approximately0.5 to 1.5 molars of potassium chloride; approximately 8 to 12millimolars of tris(hydroxymethyl)aminomethane hydrochloride; andapproximately 8 to 12 millimolars of ethylenediaminetetraacetic acid. 9.A method, comprising: providing a piece of highly oriented pyrolyticgraphite including first and second electrode contacts configured toreceive an electrical voltage, and a reaction area configured to receivea DNA sample; depositing said DNA sample on the reaction area of saidpiece of highly oriented pyrolytic graphite, wherein said DNA samplecomprises double-stranded DNA or single-stranded DNA; applying arelative humidity to said piece of highly oriented pyrolytic graphite;and applying said electrical voltage across said first and secondelectrode contacts, thereby etching a surface of said highly orientedpyrolytic graphite, wherein said electrical voltage is a voltagegradient of approximately 2 to 6 V/mm.
 10. The method of claim 9,further comprising: rinsing said etched highly oriented pyrolyticgraphite in deionized water.
 11. The method of claim 9, wherein saidfirst and second electrode contacts are positioned approximately 600 to1000 micrometres apart.